Experimental Study On Impurity Suppression In Core Region Of EAST Based On Impurity Spectroscopic Diagnostic

In a fusion device,impurities are naturally produced during operation.Due to neoclassical pinch and other effects,these impurities can be transported from the edge of the plasma into the core.However,this process also results in energy loss as the impurities radiate and cool down the core plasma,potentially leading to plasma shutdown.Therefore,understanding and controlling impurity transport is crucial for achieving long pulse and high performance in fusion devices.This thesis focuses on impurity control in fusion devices,and the following studies have been conducted on the EAST tokamak:（1）development of impurity spectroscopy diagnosis;（2）analysis of impurity spectra;and（3）experimental investigation into impurity transport.（1）In EAST tokamak,the plasma impurity measurement is the essential prerequisite of impurity transport study.The impurity spectroscopy diagnostic is an important way to measure impurity in tokamak.As the temperature of the plasma core is much higher than that of the plasma edge,the same kind impurity ions gradually increase in the ionize state from the plasma edge to the plasma core.The wavelength of the characteristic spectrum gradually decreases from long to short.In EAST tokamak,the characteristic spectrum of the plasma core is mainly concentrated in the X-ray and extreme ultraviolet（EUV）range,and the characteristic spectrum of the plasma edge is mainly concentrated in vacuum ultraviolet（VUV）and visible light range.In order to measure the edge impurity spectrum,a VUV spectroscopy diagnostic system with high time resolution and spectral resolution is developed.The VUV spectral system is normal incidence eagle type spectrometer.This VUV spectrometer with this design makes the spectrometer more compact and realize the spectral measurement with high resolution and low aberration.The VUV spectrometer change output wavelength by rotating grating and moving detector on exit axis.The system uses photomultiplier tube（PMT）and charge coupled device（CCD）to realize single spectrum measurement with high time resolution and multi-spectrum impurity spectral profile measurement,respectively.The VUV spectral system has been installed in the EAST tokamak to measure plasma edge impurity spectra.The long and short wavelength calibration have been calibrated by mercury lamp and synchrotron radiation.（2）The impurity behavior and transport need to analyze the corresponding impurity ion spectra.The high ionized state impurity spectra are used to analysis the impurity behavior and transport in the core region of plasma,and the low ionized state impurity spectra is used to analysis the impurity behavior and transport in the edge region of plasma.In recent high parameter operation of EAST,the XCS has measured shorter wavelength impurity spectra of high ionized state that are W⁺⁴⁴（3.909?）,Mo⁺⁴⁰（3.932?）and W⁺⁴⁵（3.93 3?）.In long pulse experiments,XCS system to measure the plasma core W⁺⁴⁴ impurity spectrum and plasma electron temperature and density of plasma core region severe disturbance has consistency.Therefore,the highly ionized impurity spectra measured by XCS can be used for impurity monitoring under high parameters and long pulses,which is of great significance for the study of impurity behavior and transport in the plasma core under high parameters.At present,the impurities in the plasma edge region of the EAST tokamak predominantly emit radiation within the VUV range with the enhancement of plasma parameters.Therefore,the VUV spectroscopy diagnostic system is applied to measure the impurity in the edge of plasma,and a series of impurity spectra are obtained in recent experiments.The impurity spectra in the edge of plasma measured by VUV spectroscopy diagnostic system are identified using atom data provided by National Institute of Standards and Technology（NIST）database.The results of impurity spectra analysis show that the impurity radiation in VUV range is mainly carbon impurity,and the resonance line spectral intensity of CIV 154.8nm carbon is the strongest.In experiment of the influence of resonance magnetic perturbation（RMP）on impurity transport,the time evolution of core impurity and edge impurity measured by VUV system shows that plasma core impurity radiation decreases with the increase of RMP coil current,and plasma edge impurity increase with the increase of RMP coil current.The impurity diagnostics of core and edge plasma provide the measurement of impurity behavior from core and edge plasma for impurity suppression in RMP phase.It provides a basis for further analysis of impurity transport.（3）Based on the above spectroscopy diagnostic system development and impurity spectra study,the purpose of this study is to explore the radiofrequency（RF）wave heating and RMP on the impurity removal of plasma core.In the experiment with heating power increase of electron cyclotron wave（ECW）,it is observed that the impurity decreased when the ECW reach a certain power.Experimental studies show that the axial heating of ECW needs to reach a certain threshold to suppress the impurity.In addition,in the impurity suppression experiment of RF wave and RMP,the impurity of the plasma core decreases when the RF wave power reach a certain threshold,and the impurity decrease of the plasma core is phase dependent on RMP.The time behavior of turbulence intensity and impurity intensity show that impurity intensity changes inversely with turbulence intensity when the turbulence intensity exceeds a certain threshold.And the turbulence intensity changes in direct proportion to RMP.The results of impurity transport coefficient calculated by STRAHL code show that RF wave heating and RMP enhance the impurity diffusion of the plasma edge.The RF wave suppress the inward convection velocity of plasma core,while RMP can reverse the convection velocity of plasma edge.It is found that the core and edge can be integrated to suppress impurity when the RF wave heating and RMP apply together.